1. Field of the Invention
This invention relates to an indirect bonding tray that is used for placing orthodontic appliances on the surfaces of a patient's teeth. More particularly, the present invention is directed toward a method and an assembly for making an indirect bonding tray.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to desired locations in the oral cavity. Orthodontic treatment can improve the patient's facial appearance, especially in instances where the teeth are noticeably crooked or where the jaws are out of alignment with each other. Orthodontic treatment can also enhance the function of the teeth by providing better occlusion during mastication.
One common type of orthodontic treatment involves the use of tiny, slotted appliances known as brackets. The brackets are fixed to the patient's teeth and an archwire is placed in the slot of each bracket. The archwire forms a track to guide movement of teeth to desired locations.
The ends of orthodontic archwires are often connected to small appliances known as buccal tubes that are, in turn, secured to the patient's molar teeth. In many instances, a set of brackets, buccal tubes and an archwire is provided for each of the patient's upper and lower dental arches. The brackets, buccal tubes and archwires are commonly referred to collectively as “braces”.
In many types of orthodontic techniques, the precise position of the appliances on the teeth is an important factor for helping to ensure that the teeth move to their intended final positions. For example, one common type of orthodontic treatment technique is known as the “straight-wire” technique, where the archwire lies in a horizontal plane at the conclusion of treatment. Consequently, if a bracket is attached to the tooth at a location that is too close to the occlusal or outer tip of the tooth, the orthodontist using a straight-wire technique will likely find that the tooth in its final position is unduly intruded. On the other hand, if the bracket is attached to the tooth at a location closer to the gingiva than is appropriate, it is likely that the final position of the tooth will be more extruded than desired.
In general, orthodontic appliances that are adapted to be adhesively bonded to the patient's teeth are placed and connected to the teeth by either one of two techniques: a direct bonding technique, or an indirect bonding technique. In the direct bonding technique, the appliance and adhesive are grasped with a pair of tweezers or other hand instrument and placed by the practitioner on the surface of the tooth in an approximate desired location. Next, the appliance is shifted along the surface of the tooth as needed until the practitioner is satisfied with its position. Once the appliance is in its precise, intended location, the appliance is pressed firmly onto the tooth to seat the appliance in the adhesive. Excess adhesive in areas adjacent the base of the appliance is removed, and the adhesive is then allowed to cure and fix the appliance firmly in place.
While the direct bonding technique described above is in widespread use and is considered satisfactory by many, there are shortcomings that are inherent with this technique. For example, access to surfaces of malposed teeth may be difficult. In some instances, and particularly in connection with posterior teeth, the practitioner may have difficulty seeing the precise position of the bracket relative to the tooth surface. Additionally, the appliance may be unintentionally dislodged from its intended location during the time that the excess adhesive is being removed adjacent the base of the appliance.
Another problem associated with the direct bonding technique described above concerns the significant length of time needed to carry out the procedure of bonding each appliance to each individual tooth. Typically, the practitioner will attempt to ensure that each appliance is positioned in its precise, intended location before the adhesive is cured, and some amount of time may be necessary before the practitioner is satisfied with the location of each appliance. At the same time, however, the patient may experience discomfort during the procedure and have difficulty in remaining relatively motionless, especially if the patient is an adolescent. As can be appreciated, there are aspects of the direct bonding technique that can be considered a nuisance for both the practitioner and for the patient.
Indirect bonding techniques avoid many of the problems noted above. In general, indirect bonding techniques known in the past have involved the use of a placement device or transfer tray having wall sections with a shape that matches the configuration of at least part of the patient's dental arch. Often, the tray has a generally “U”-shaped channel for receiving a number of teeth simultaneously. A set of appliances such as brackets are releasably connected to the tray at certain, predetermined locations within the channel.
During the use of orthodontic transfer tray for indirect bonding, an adhesive is typically applied to the base of each appliance by the orthodontist or a staff member. The tray is then placed over the patient's teeth and remains in place until such time as the adhesive hardens. Next, the apparatus is detached from the teeth as well as from the appliances, with the result that all of the appliances previously connected to the tray are now bonded to respective teeth at their intended, predetermined locations.
In more detail, one method of indirect bonding of orthodontic appliances using the transfer tray described above includes the steps of taking an impression of each of the patient's dental arches and then making a replica plaster or “stone” model from each impression. Next, the appliances are bonded to the stone models at desired locations. Optionally, the bonding adhesive can be a chemical curing adhesive (such as Concise brand adhesive from 3M) or a light-curable adhesive (such as Transbond XT brand adhesive or Transbond LR brand adhesive from 3M). Optionally, the brackets may be adhesive precoated brackets such as those described in U.S. Pat. Nos. 5,015,180, 5,172,809, 5,354,199 and 5,429,229.
The transfer tray is then made by placing a matrix material over the model as well as over the appliances placed in the model. For example, a plastic sheet matrix material may be held by a frame and exposed to radiant heat. Once the plastic sheet material has softened, it is placed over the model and the appliances. Air in the space between the sheet material and the model is then evacuated, and the plastic sheet material assumes a configuration that precisely matches the shape of the replica teeth of the stone model and attached appliances.
The plastic sheet matrix material is then allowed to cool and harden to form a tray. The tray and the appliances (which are embedded in an interior wall of the tray) are then detached from the stone model. If the cured adhesive that was used to bond the appliances to the stone model remains on the base of the appliances after detachment from the stone model, the adhesive serves as a “custom” base having a concave contour that precisely replicates the convex contour of the previous attachment location of the stone model, as well as the convex configuration of the intended mounting location of the appliances on the patient's teeth.
Once the patient has returned to the practitioner's office, a quantity of adhesive is placed on the base of each appliance, and the tray with the embedded appliances is then placed over the matching portions of the patient's dental arch. Since the configuration of the interior of the tray closely matches the respective portions of the patient's dental arch, each appliance is ultimately positioned on the patient's teeth at precisely the same location that corresponds to the previous location of the same appliance on the stone model.
In recent years, many improvements have been made in the field of indirect bonding. For example, U.S. Pat. No. 5,971,754 describes a two-component indirect bonding adhesive with a relatively fast curing time that reduces the length of time that the tray must be firmly held against the patient's teeth. U.S. Pat. No. 6,123,544 describes a transfer tray that receives movable arms for placing appliances on the patient's teeth once the tray is positioned in the oral cavity. Published U.S. patent application entitled “METHOD AND APPARATUS FOR INDIRECT BONDING OF ORTHODONTIC APPLIANCES” (U.S. Publication No. 2004-0219471, published on Nov. 4, 2004), describes among other things a transfer apparatus with an improved matrix material for releasably holding appliances in place. Published U.S. patent application entitled “APPARATUS FOR INDIRECT BONDING OF ORTHODONTIC APPLIANCES AND METHOD OF MAKING THE SAME” (U.S. Publication No. 2005-0074716-A1, Apr. 7, 2005 describes among other things a transfer apparatus that includes at least one appliance having a base with a contour that is a replica of a contour of a portions of the patient's tooth structure, and a bonding composition on the base for bonding to the patient's tooth structure.
Indirect bonding techniques offer a number of advantages over direct bonding techniques. For one thing, and as indicated above, it is possible to bond a plurality of appliances to a patient's dental arch simultaneously, thereby avoiding the need to bond each appliance in individual fashion. In addition, the transfer apparatus helps to locate the appliances in their proper, intended positions such that adjustment of each appliance on the surface of the tooth before bonding is avoided. The increased placement accuracy of the appliances that is often afforded by indirect bonding techniques helps ensure that the patient's teeth are moved to their proper, intended positions at the conclusion of treatment.
However, the ultimate location of the appliances on the patient's teeth during an indirect bonding procedure is determined by the earlier, temporary location of the appliances on the replica teeth. Consequently, it is important to ensure that the appliances are precisely placed on the replica teeth at the correct, pre-determined locations. The above-mentioned U.S. Pat. No. 5,971,754 describes a method of marking the replica teeth with a pencil using a gauge to determine the location of the pencil mark, and the appliances are subsequently aligned by eye to the pencil mark and then visually checked to ensure accurate placement.
As alternative to manual placement of appliances, a computer controlled robotic arm may be used to grasp each appliance in sequence and place it on the associated tooth. For example, if the replica dental arch is made using digital information, a computer may be used to calculate an idealized position for each appliance on the patient's tooth, and that information can then be used in a set of instructions to control movement of the robotic arm such that the appliance is placed on the corresponding, selected location of the associated replica tooth. With this method, the use of pencil marks for visual alignment of the appliances may be avoided.
However, the use of a robotic arm to place appliances on replica teeth presents difficulties in the manufacturing process of making the trays. For example, there are a vast number of different orthodontic appliances, each having a unique shape and prescription, and the particular appliance selected will often vary from tooth to tooth, from patient to patient, and from practitioner to practitioner. Consequently, it would be a somewhat expensive task to set up an automated system for feeding the appliances to the robotic arm due to the large number of available appliances that may be needed for any particular patient. Moreover, it may be difficult to construct a set of universal jaws for the robotic arm in order to pick up each appliance, as the external shape of the various appliances may greatly differ.